Origin

Early 19th century: of unknown origin. Early use was as a noun denoting a horse of little value, later applied to a poor white in some Southern states of the US, hence 'shabby, cheap, in bad taste' (mid 19th century).

The origin of tacky in the sense ‘sticky’ is from the word tack (Middle English) ‘to fasten lightly’, or for an object that does that job. The origin of this word is obscure. The sense of tacky meaning ‘in poor taste, cheap’ is different, but equally obscure. It was first found at the beginning of the 19th century in the USA meaning a weedy horse. By the late 19th century it was applied to a poor white in some southern states, and had also acquired its modern sense. The shortening tack did not happen until the 1980s. The sense tack for horses equipment is a shortening of tackle.

tackiness

I urge you all to grab a camera and go riding through the night, spying on your gaudy neighbors, as I will award a prize to the person who sends me the picture of the most horrible display of Christmas tackiness.

In some of the wealthier suburbs over there, they get in electrical contractors to do a professional lighting job on their houses and, unfortunately, tackiness often wins out over good taste.